Study On Preparation And Densification Of As-cast Aluminum Alloy Tubular Preform

Casting aluminum alloys are widely used in automotive, rail transportation and other fields owing to their good castability,high specific strength and low cost. But the casting alloys are easy to hydrogen oxidation, And there are porosity, shrinkage, pinholes, porosity and other defects in the casting process.The casting aluminum alloys are difficult to become fully dense because of these defects, which seriously affects the strength and toughness of casting aluminum alloys.They can not meet the requirements of components. Because of the restriction of equipment and cost, it is difficult to carry out the subsequent processing and densification of large-size tube. In order to reduce or even eliminate the defects of the casting alloys, we investigate two types of casting aluminum alloys, Al-Si and Al-Zn casting aluminum alloy. the Al-7Si (A356), Al-12Si, Al-20Si and ZL401 alloy tube are prepared by means of the traditional gravity casting technology. A new wedge pressing process was adopted based on the idea of accumulating local small deformation as to integral forming. The rule of the wedge pressing process and microstructures and mechanical properties of the alloy were investigated by hardness test, tensile test and SEM. The following conclusions:1. Al-7Si (A356), Al-12Si, Al-20Si and ZL401 casting aluminum alloys are prepared by gravity casting. The wedge pressing process is first applied in the casting tube. Densification process of casting aluminum is achieved on a small tonnage equipment.The alloy tube with overall high-density, round shape, and good mechanical properties is obtained .2. The tensile strength , the yield strength ,elongation and the relative density of gravity casting of A356 alloy can reach 224MPa, 201MPa, 7.3% and 99.6%, respectively compared with no wedge pressing,which is 148MPa, 133MPa, 2.5%, 95.6%, respectively. The pinholes are lost after wedge pressing. The porosity and loose of Al-12Si casting alloy reduce markedly or even eliminate. The tensile strength and yield strength of Al-12Si casting alloy increase to 197MPa and 172MPa respectively coMPared with no wedge pressing.which is 142MPa and 113MPa respectively. The elongation of Al-12Si casting alloy is 1.7% before wedge pressing.By contrast,it can rise to 5.5% after wedge pressing.Similarly, the tensile strength,yield strength, elongation and hardness of Al-20Si casting alloy increase from 112MPa, 82MPa, 1.2%, 2.48g/cm3, 59.3HB to 203MPa, 172MPa, 5.2%, 2.68g / cm3, 71.5HB, respectively after wedge pressing are up to 197MPa, 172MPa and 5.5%,respectively through wedge pressing.Also, the fracture mode transfer from brittle to ductile fracture.The primary silicon is broken and distribution on the matrix equably.3. The microstructure of ZL401 casting alloy is improved sharply.The size of hole in the casting alloy decreases from 80μm to 3-5μm or even disappear after wedge pressing.The mechanical properties of ZL401 alloy is from 161MPa, 3.3% increased to 232MPa,7.2%,respectively.